An important part of each solar panel is the “absorber”, which in most cases is made of an absorber sheet and a riser. The riser often comprises one or more pipes, for example with a diameter between 6 to 12 mm and corresponding collecting pipes, for example of diameters between 15 and 40 mm. The said pipes may be smaller or bigger, depending on the collector type.
A known riser/pipe arrangement is designed similar to a “harp”, wherein several risers are arranged, parallel to each other, between two collecting pipes. In another embodiment the risers following the collector pipe, are arranged in a meander-like shape.
If not disclosed otherwise or self-evident from the context, the following disclosure refers to a complete solar panel in its use position, especially with its transparent upper side towards the sun.
While solar panels for private purposes to support a warm water and heating water demand in a temperature range up to approximately 50° C. are mostly designed in a basic construction, often with just one ordinary cover (mostly made of glass) on its side facing the sun, much hotter water is needed for industrial/commercial purposes, for example to support a district heating network.
Insofar a better thermal insulation is required for these panels to reduce possible heat losses of the panel, in particular by convective flow.
A known system provides for a transparent foil between the transparent cover and the absorber sheet. The said foil is used to interrupt any convective flow and thus any heat transport to the glass pane. It is a disadvantage of this system that the said foil must be strained to avoid any contact with the absorber. It was also realized that the said foil may tear.
Another known embodiment uses a double glazed cover instead of a single glazed one. The double glazed version can be realized as an insulating pane (the intermediate space filled with a gas) or with air between the two glass panes. The use of an insulating pane is critical as the temperatures within the collector housing (collector space) may become very high and may not be controlled any more. This design is therefore not suitable for a mass production with guarantees of up to 10 years.
With an embodiment using air between the glass panes, the following could be observed: The different temperatures adjacent to both glass panes cause different thermal expansions of both glass panes, while the glass panes are prevented from expanding differently by the gas tight connection. The tensions may be that high, that the double pane bursts.
Another disadvantage is that moisture (condensate) can accumulate between the panes. Because of varying temperatures in the collector space the pressure in said space between the panes varies. This collector type must further withstand other compression and tension forces, caused by wind and snow loading, which may be as high as 600 kg/m2.